Hollow composite panels are used in a large number of structures. In particular, horizontal panels are used as flooring and vertical panels are used to produce separations in the fields of structural engineering, industrial construction, and in the transportation field (particularly shipbuilding, truck construction and aircraft construction).
In the case of horizontal panels used in the transportation field (boat deck, truck floor), there is a strong advantage in reducing the weight of the panels so as to contribute to a reduction in the total empty weight and to thereby enable savings in fuel, an increase in the weight transported and/or increased speed.
FR 1 024 889 discloses a plurality of geometries for hollow composite panels including two walls held by separating parts consisting of thin corrugated or embossed metal sheets or the like, running uninterruptedly over the entire surface of a panel element.
The use of metal sheets does not make it possible to achieve sufficient degrees of mechanical strength for the most demanding constructions.
U.S. Pat. No. 6,574,938 (Donati) discloses a sandwich panel including at least one sheet and at least one fretted element the size of which is substantially similar to that of the sheet and the cross-sectional profile of which has a succession of adjacent trapezoidal patterns. The method of manufacture includes a step for winding the fretted element, which is difficult to consider for thick metal, which limits the application of this invention in terms of mechanical strength.
FR 2,207,581 (Wendel-Sidelor) discloses a hollow steel slab made of two plates held at a distance by U-shaped connecting elements and lined by watertight side elements, all elements being adhesively bonded.
EP 0 589 054 (Nippon Steel) discloses stainless steel honeycomb panels comprising a corrugated sheet or parallel groove materials.
WO 02/32598 (Kujala et al.) discloses a metal sandwich structure comprising a core which consists of a plurality of individual honeycomb sections spaced from each other, and a first and second cover panel attached to the sections by laser welding, the cover panels having their skirts brought to the proximity of each other by means of deflections.
In these inventions, the benefit of the use of aluminum is not considered. The use of aluminum to produce this type of panel, in place of denser materials such as steel, can, however, enable an appreciable weight reduction.
EP 1 133 390 (Corus Aluminum) discloses a composite aluminum panel comprising two parallel plates and/or sheets secured to the peaks and troughs of a corrugated aluminum stiffener sheet preferably via welding. One particular alloy (an alloy of the 5XXX family, containing zinc) was selected for the manufacture of the corrugated sheet. The mechanical strength properties of the panel obtained are not specified.
Another alternative is to produce a panel by welding hollow structural members. EP 1 222 993 A1 (Hitachi) thus discloses the assembling of hollow shape members by welding in order to produce a panel. This technique has the disadvantage of requiring numerous joining operations due to the limited width of the hollow shape members, which weakens the structure. In this same patent application honeycomb panels comprising edge members joined by friction stir welding are also disclosed.
The disadvantages of existing metal panels are many. In the methods including a fusion welding step, a sometimes unacceptable deformation of the panels occurs. Furthermore, when an intermediate sheet is used, the mechanical strength of the panels is limited by the characteristics of the intermediate sheet. As a matter of fact, it is difficult, and would require a costly investment, to obtain corrugated or fretted sheets from thick sheets, such as, in particular, sheets the thickness of which is greater than 1 mm or even 2 mm. Prior art panels are substantially symmetrical transversally and/or longitudinally although it would be desirable to be able to easily customize, as needed locally, the mechanical strength of the panel to the stresses that it will have to undergo, so as to optimise the local compromise between its weight and its mechanical strength.